Review on Hydrotac OPTX 20/20 Stick On Magnification Bifocal Lenses - Reusable +2.50 Diopter (Pack of 2) by Jennifer Roberts

I've tried several brands of these things. These are NOT Fresnel lenses like the very first set I tried many years ago. They are much better visually and cosmetically. So far they seem to be the best for my purposes in terms of quality and adhesion. How you install is important. 1) Wash everything with soap and water. 2) Apply a puddle of water to the inner surface of the lens. 3) Throw this thing in that puddle - the water should cover it. 4) Slide it across the puddle until you find the right spot - it may take a few tries. 5) Turn jars upside down and allow excess water to drip off - DO NOT wipe. 6) Allow jars to dry intact for 24 hours on an absorbent towel to catch drips. 7) After 24 hours, hold them in the light - there should be few, if any, visible bubbles or adhesion will suffer. I found the adhesion to be pretty good after doing all the above steps. I can wash my glasses as usual with soap and water and then dry them thoroughly with an absorbent cloth. The pads stay in place. Pretty cool. Note: They have a distinct curvature. I doubt they will ever stick to the outside of goggles (I've tried unsuccessfully) or to a flat surface like a snorkel mask (there are other brands that can). And it's entirely possible that the curvature/shape/mounting of your lenses doesn't match that curvature well. Also note that while there are others, bifocal lenses come in two standard sizes - D28 and D35 - with D28 being the most common. Standard I think. The "D" refers to the shape that is obvious to them. The next number refers to the width of the lens (in mm) at its widest point, which MAY NOT be at the top. In this case it looks like this. And I measure mine at around 28mm. I'm not sure if there are wider sticks. But if you need it or care about it, ask first. Overall, I'm not sure they're as "good" as custom bifocals, as there are many factors to consider. But it's a good, inexpensive way to test things and see how they work for you before taking the plunge. And for some, they might be all you need.